As the boundaries blur, we have increasingly been asked to work on multimedia projects, such as small cinemas, cinemas in super yachts and this – the hardest one so far:

A theatre. A cinema. A 7.1 mix room. All at the same time.

Composer, film director and all round nice guy Tony Britten (best known to you perhaps for his UEFA Champions League Anthem) pitched me an interesting and complex challenge last year: ‘ Can you take this little old barn, and convert it into a 50 seat private movie theatre and performance venue, that is also accurate for mixing 7.1 stems for movies?’

That’s not as simple as it sounds.

It has to have a ventilation system that can cope with the CO2 and heat of 50 people, yet quiet enough to mix a pin dropping. And accurate. And not to look like a Studio (Tony said!)

I hope you think we succeeded! Design by yours truly. Construction by the ever reliable master craftsman Jeff the Builder…

We enlisted the assistance of a brilliant a/c consultant and retained the ‘look’ of the barn (It had previously housed 2 old theatre organs and been lined in wood by the previous owner.) Ventilation plenums were hidden behind said panelling as was bass trapping.

My first experience of the finished building (after testing) was the private premiere of Tony’s latest film ‘Chick Lit‘. The pre – film piano concert sounded great and the 7.1 rendition as I had expected! Also, no-one got too hot on a warm summer evening with every seat occupied. That’s what we are there for!

The Author.

Howard Turner has over 30 years experience in the studio business, and for the last two decades his Studio Wizard Organisation has allowed him to stop shouting at musicians and going to sleep on the mixing desk all of the time, instead he gets to design studios and shout at builders for a change…

Sorry for the lack of posts recently! The first half of 2017 has sped by, and in the process I’ve had the chance to design and help build some great facilities that I’d like to share with you.

This first one is Orange Tree – built for a company called AmpFactory in East Anglia, UK. Designed by yours truly and built by the ever impressive Jeff the Builder, who has been building studios with me since the early 90s.

The Author

Howard Turner has over 30 years experience in the studio business, and for the last 2 decades, his Studio Wizard Organisation have been at the forefront of the development of effective & affordable designs and solutions for studios.

If you’ve ever built a home studio, you’ll have read much advice on the ‘net about Bass Traps….

When I built my first studio, way back when reverbs had springs in and autotune involved someone else, your guitar and a tuning fork, I got my first advice about bass traps.

Control Freak.

The back of the room with the speakers in – we called it the Control Room, although the last thing you could describe its acoustic as was controlled – suddenly turned the track you were listening to into a dub reggae version if you put your head against the back wall. In fact, if dub reggae was what you were aiming for, you listened to the back wall version, then tried to replicate it in the middle of the room.

An old lag in the industry who ventured into my domain told me: “what you need is a bass trap mate”.

Thus inspired, I ventured to find this holy grail, this ‘bass trap’ that would make my room sound perfect, and remove the ghost of Bob Marley from my back wall…

Set me free.

Legions of engineers since have been confronted by the same paradox – something that traps bass yet simultaneously makes it true and free. Much has been written about this magical treatment and much has been bollocks. My favourite being the wonderful flash animation on an alleged ‘professional studio builders’ page a few years ago that illustrated a bass trap as the ‘thing you put over the windows to stop the bass getting out’.

The truth is, sadly, much more mundane. It turns out that in a conventional room, the sort that we all live our lives in, most of the bass ends up heading out via the doors, windows and ceiling, leaving precious little to bounce back and cause us trouble when we are listening to music.

Not none, of course. Any room with parallel walls will conspire to boost some frequencies, and wipe out others, with the unfortunate characteristic of doing this sneakily and almost indiscriminately depending on where you are in the room.

However, when isolation is required and you try to trap sound in a room (or keep it out), the effect is magnified by a at least an order of magnitude, and the peaks and troughs can become so excessive as to render your perception of what is coming out of the speakers more or less meaningless…

Show me the way?

So, what to do? Well in recent years, since the advent of the ‘net, a host of advice has found its way onto google. Sadly, much of it is touted as generic – ie proposed as something that will work for everyone – when the reality is that every room is different, and every room will require trapping tuned to that room’s particular anomalies.

Lets face it – where was anyone going believing that all these problems had a universal solution? Did anyone really think that someone’s total lack of bass and another persons huge boom at 100hz were going to be resolved by application of the same bass treatments?

Heal me!

Funnily enough – it turns out that the problems, and the solutions, can be more than just varied. The problems can stem from many sources.

Likely causes:

Parallel walls- these cause peaks, and troughs (depending on where you are in the room) that distort at specific finely defined frequencies.

Weak walls – these will leak bass, causing poor bass response, either at specific frequencies, or wideband across the spectrum.

Strong walls – these will reflect the bass as part of keeping the sound in or out, causing peaks and nodes that vary depending on the offset of the barriers.

Weak doors allowing the influence of:

External spaces such as corridors – where the tube-like construction sets them up like tuned ‘organ pipes’ hanging off the room, and creating complex harmonic sequences of boost and cut that initially completely confuse the situation.

Then there are the secondary causes:

Poor speaker mounts – resonating at some frequencies and not others – upsetting the sound before it even leaves the cabinet. Especially where speakers are resting on the top of nice symmetrical wooden furniture – and don’t get me started on ‘monitor walls… 🙂

Speakers sat one on top of the other – physical contact causing the speaker not in use to act as a limp membrane absorber to the one in use, causing what may be huge response suck-outs in the order of tens of dB…

Rock n Roll Doctor:

I frequently attend studios where the poor bass integrity has encouraged the client to purchase more and more bass ‘solutions’ – to the point where there may be no bass left to solve. I have been seen dragging expensive bass trap panels out into driveways to undo the damage caused.

Worse, is the tendency for companies peddling acoustic ‘solutions’ to market generic bass traps as suitable for any environment. These tend to come in two flavours – either the fixed centre frequency bass trap – often centred at 100Hz – that is sold as a universal panacea, or a wide band bass trap – often claimed to operate over a huge band – usually 100-600Hz, which, when assessed in situ, affects hardly any of these frequencies to any significant degree.

Dr Robert?

Why are these fake solutions peddled by modern day snake-oil salesmen?

Well, a few years ago, all of us in the audio industry were fixated on buying small boxes of electronics – reverbs, midi sound modules, compressors etc., that we were convinced would transform the output of our studios. When those wonderful magic boxes were replaced with cheap virtual plug-ins, an entire generation of distribution companies and salesmen were cast adrift from the good ship audio. Bearing in mind that only a fraction of those could find employment designing, manufacturing and selling us Microphones and Speakers (the last physical interfaces that we couldn’t avoid) then the rest turned their efforts towards selling us things that modified our rooms acoustically.

Sadly, apart from soft panels that make the midrange sound better (or get rid of it and make it sound worse, but that’s another story), any effective bass trapping these chaps could sell was going to be either too bulky, too heavy or too room specific to be a mass market product. That didn’t stop them. They made the products anyway – even if they didn’t work. They made them light – so they could ship. They made them small – so they could ship. They made them all the same – so they could be mass-produced. What they didn’t do is make them heavy, bulky and individual – so that they would actually work for YOUR room.

Here are some results from a room boasting £500 of proprietary light-weight bass traps (the sort that look, and feel, like an expensive mattress) – note that when we removed them, the change in LF response was minor and restricted to a tiny change in the lower mid – nowhere near the claims made by the product.

With proprietary bass trap.

Without bass trap.

I think the results are self explanatory.

Embrace the difference:

Just like we as humans are all different, then so are the rooms we listen to music in all different. They require different treatments to achieve the same result – the universal monitoring environment we all crave. No one says that environment is easy to achieve, but we can all agree that it is not achieved by application of some simplistic, universal treatments.

A comedy of errors:

So, why can we not simply adjust the response of a room by using a graphic equaliser or a digital room correction algorithm? Well, our ears are fine tuned by millennia of training, to separate out direct sound from an object from the reflected ‘reverberant’ sound produced on the way to the ear. Sadly microphones – and analysis software – do not have this ability. In their crude attempts to ‘flatten’ the response, such systems lump both direct and reverb sounds together and attempt to equalise the amalgam of the two. The result, to our much more sophisticated ears, is a signal now not only twisted by reverberation from reflections, but also by apparently random dips and peaks in the direct response, as the system attempts to correct in a manner as crude and inappropriate as a Victorian electrician trying to fix an iphone.

In conclusion:

You have three choices:

Live with it.

Get someone who knows what they are doing to diagnose it and prescribe a correction.

Gain the experience to correct it yourself.

Now, given that your reading this because 1) is unacceptable, I’m not about to advocate 3) when I can offer 2) for a sum far lower than the cost of one of those traps that don’t work – am I?!

The Author

Howard Turner has over 30 years experience in the studio business, and for the last 2 decades, his Studio Wizard Organisation have been at the forefront of the development of effective & affordable designs and solutions for studios. Further information: +447803666789 web: www.studiowizard.com

When is a recording studio not a recording studio? When it’s a bog-standard classroom with some gear in! Howard Turner from Studio Wizard looks at what it takes to make a proper educational audio facility, and how recent regulations should have spelt the end for shoddy school studios.

If your PE teacher was given a swimming pool full of mud, and told that this was the ‘new purpose built facility for gymnastics’, you’d probably forgive that colleague for getting more than a little upset! However at the commencement of each term, we get calls from schools and colleges where equally inappropriate spaces have been foisted on Music Departments claiming to be ‘Recording Studios’. We know it’s wrong, you know it’s wrong, and now the government have given us the means to do something about it!

Since July 2003, new approved Document E of Building Regulations came into force. Since…

This was originally written with school music departments in mind, but frankly, all the techniques involved will work for anyone!

It’s a fact of life that the majority of spaces used for music recording, listening and mixing are less than perfect. Although the current regulations encourage new build facilities in education to be fit for purpose, they rarely are – and what about the rest? Well there is hope, and in the coming paragraphs I hope to show you how to significantly improve the sound of your room(s) without breaking the budget!

Firstly – a quick lesson in definitions: There are 4 significant issues that affect the usability of a room for sound recording or mixing.

Room Shape – the cause of odd noises such as booming low notes and flutter echoes between parallel walls.

Now some of these are simply not addressable without major engineering. Certainly if the library next door complain about your drum lessons then its time to move the department! Isolation works are major construction issues; there is NO quick fix – NO simple stuff you can ‘stick on’ the walls to stop the noise.

However for the rest, there are some simple experiments and tricks that will yield considerable improvements – let’s start with the most common:

Rattle & Roll

Most of the issues to do with intelligibility are caused by High Frequency (HF) reverb – typically above 500hz. If you are attempting critical listening in a reverberant environment chances are that apart from students immediately in front of the speakers the rest are hearing more of the room than the speakers! Solutions however are simple.

Prove you can improve matters: Hang some borrowed sleeping bags or duvets on the walls or hang them over microphone boom stands set up in a T shape – try to cover at least 1/3 of the wall area – this should radically improve matters and should allow you to demonstrate to whoever holds the purse strings that you need to invest in some sound deadening panels made of sheepswool or rockwool slabs. You can experiment with positioning so you know where best to fix the panels when you buy them – note most foam panels are hard to fix permanently, are easy to damage, and often do not have the smoke/fire rating for an education environment so are not recommended.

Consider carpet: Hard floors not only reflect noise – they cause it – shuffling feet and chairs are huge distraction. The simple act of laying industrial grade carpet or carpet tiles can help a lot by minimising these noises and also helping reduce the reverb time of the room. However – beware of thinking this means you can use them on the walls! A carpet tile only absorbs sound over a narrow range of frequencies – so the effect of completely carpeting a room can leave mid frequencies unchecked and actually sound worse than an untreated room! Also – if your recording space suffers footfall noise from classes above – simply carpeting the offending space may remove the problem just as effectively as isolating your classroom!

Work closer: If you can get the speakers and students into the same 1/3 of a room then a lot of the main reverberation effects – especially at lower frequencies – will be in the unused part of the room. This isn’t a permanent fix, but certainly can be used quickly to improve matters when one is required to teach in unsuitable spaces.

Flutter can be dealt with in exactly the same way as the HF reverb – by placing soft panels on the walls. The most efficient arrangement is as a checkerboard pattern on each facing wall with one wall being the inverse of the other, i.e. each soft panel facing an untreated bit of wall opposite.

Boom is caused by what is called the ‘axial modes’ of the room – i.e. the 3 parallel dimensions of a rectangular room each exhibit a note – a bit like an organ pipe. For example 11 feet will give a note of approx 100hz (roughly where all the bass detail in rock music is centred), 22 feet – 50hz etc etc. Sometimes the problem is worsened by dimensions of the room being all the same (cubic) or harmonic multiples of each other (e.g. twice as long as high etc). The bad news is that these cannot be properly removed without reshaping the room, however, once the problem frequencies are known, and the offending dimensions identified, it is possible to build and place specifically tuned bass traps in such a way as to minimise the problems. The measurement of such issues requires the services of a studio acoustician; however the construction and placement of the traps should be well within the capabilities of the average school handyman or woodwork department.

It is now accepted that good schoolroom acoustics are a major contributing factor to the learning experience all through the school – not just in the music department. However – it is in music that the inadequacies of building design are thrown into starkest relief. The government provided guidance to all these requirements in 2003 in Building Regulation BB93 – however this regulation is only a statutory requirement in new build projects, not renovations. The good news however is that all these issues outlined above can be dealt with in the design stage, and frequently the cost of implementing good acoustic design can be barely more than that of ordinary construction.

In the meantime however a little ingenuity and rockwool can go a long way….

The Author

Howard Turner has over 30 years experience in the studio business, and for the last 2 decades, his Studio Wizard Organisation have been at the forefront of the development of effective & affordable designs and solutions for studios. Further information: +447803666789 web: www.studiowizard.com

Originally written as a useful ‘how-to’ for an old Aces 24track 2″ tape machine, this guide will work well with most other machines, as the Aces has more eq control than most, so you’ll probably find your machine has less eq settings to tweak.

1). Demagnetise the heads.
Turn off the machine!
Danger! – keep demag away from test tape and other sensitive
material – switch on and off well away from everything! Power up the demag and
bring it (slowly) up to the heads. Move it (nearly touching the head) in a zig-zag from top
to bottom and then vertically up the head over the head gap. Move slowly to the next
head and repeat. Now pull it away slowly and when 3′ or more away – unplug.

2). Repro alignment.
Clean the heads. Lace up the test tape, select the 30ips AES section. Connect the
frequency counter to the o/p of any channel of the m/c. Hit play and listen to the
1k tone – if the Freq counter doesn’t say 1k, adjust the speed control until it does! –
(do the same for 15ips – while you’e at it).
Connect the RMS vvm to ch8 o/p. Play the 1k tone. I suggest we set the machine to a
400nWb/m operating level, meaning that a 320nWb/m test tape should read -2dB on
machine meters – or +2dBm on a true RMS one…If needed – set the azimuth at
this point by putting all channels into play and pushing all faders up in centre position
mono. Play the 15k tone. If you now move the head by tweaking one of the sideways
adjusters, you will see a single peak of response. This corresponds to in-phase azi
adjustment.
Do the same for the sync head.
Now select play head and play 1k(level), 15k(hf) and 60hz(lf) and set the response to -2dB
on the vu’s (equiv to +2dBM).
Use the True RMS on ch8 to check this.
(We cannot be sure the machine meters are telling the truth so if we get a channel right
by using the true rms, then we can copy that setting across and be sure it’s right (assuming
the vu’s are OK!!).

Select the sync head and do the same.

3). Rec/Rep alignment.
Clean the heads.
Lace up the blank tape.
Put 8 channels into record.
Replay off the repro (play) head.
Using your Oscillator choose 10khz and set an o/p of around 5dB below 0.
Run the tape in record.
Use the tweaker to reduce bias (anti clockwise) – watch the o/p rise to a peak and then fall.
Increase bias (clockwise) and keep increasing it past the point where the o/p hits a peak
and starts to fall.
Take it ‘over the hill’ 1-2dB (30ips), [3-4dB (15ips)].(You will need the true RMS voltmeter
to do this).

Now put an oscillator input in of 1khz(level) @ 0dB (i.e. +4dBm) – the same should come out.
Ditto at 10khz(hf), 4khz(mf)(if you adjust this you will need to check 10khz again),
and finally 100hz(lf) which should read +1dB (i.e. +5dBm).(M/c meters ok for this).
Now put the next 8 channels into record and do it all again!!
Finally, put all channels in record and listen to the o/p’s individually – there should
be no excessive or different noise on any one track.

Congratulations! Your machine is now lined up and ready to go!

The Author

Howard Turner has over 30 years experience in the studio business, and for the last 2 decades, his Studio Wizard Organisation have been at the forefront of the development of effective & affordable designs and solutions for studios. Further information: +447803666789 web: www.studiowizard.com

Studio Acoustics

How and why does sound move around your studio? Howard Turner from Studio Wizard explains some theories about sound, and looks at the basic techniques that can be used in any studio to create a great sounding room.

Most of us in the music business have a pretty good grasp of how sound behaves and what that means to us as musicians and recording engineers. We can manipulate sound in a PC or via a desk, but what about when it comes to physically manipulating the sound in a room? Or perhaps trying to stop the sound travelling from one area to another? That’s a whole new ball game.

Lets clear something up. These two issues are not one and the same thing.

Trying to make a studio sound good and easy to mix in: that’s best described as ‘room acoustics’

Ensuring you don’t keep the neighbours awake whilst tracking / mixing: that’s ‘isolation’. They may be related, but they are entirely separate matters physically. Once you’ve ‘isolated’ and trapped all the sound inside a room; it’s going to rattle around in there and sound awful unless you do something about the ‘room acoustics’.

Isolation.

For anyone with a studio, isolation is probably the first of these to occur to them, as the studio gets busier – and louder (or indeed if your neighbour suddenly decides to join in with some DIY hammering and drilling when you’re in the middle of some important vocal parts!). So what’s to be done?

The tools available to you are just the same whether you are a multi-million pound pro facility, or a bedroom studio.

Firstly we need to stop sound travelling in or out through the air – so we need to make the room airtight. Lets seal up all the air holes, put good seals on the doors and windows. This is very important – knock a one-inch air hole in a 60dB isolation wall and you’ll discover that it has suddenly become a 20dB wall! It really does make that much difference, so hunt out every crack and get busy with the filler.

Secondly we need to make sure that the walls/floor/ceiling/doors/windows are stiff enough that they don’t vibrate and transmit sound through them. Now it starts to get a bit trickier: we’re into double glazing windows, fitting double ‘soundlock’ entry doors and increasing mass by adding extra layers of plasterboard to walls etc.

These two are easy enough to achieve, and will get rid of most mid and high frequency leakage but the third tool at our disposal is the real key to successful wide band isolation, and the hardest to achieve: Decouple the noisy room from the rest of the building. This entails building an entirely separate ‘floating room’ – incorporating elements of the first two criteria – which is not fixed to the existing structure whatsoever, and sits upon some bouncy material (such as Rockwool) to keep it isolated even from the floor.

If we’ve done the best we can with the existing structure in terms of air-tightness and rigidity, and then we drop a floating room inside it, we can achieve startling levels of isolation, even at low frequencies. Just remember that it’s going to be air tight, and probably the best insulated room you’ve ever seen. So if something isn’t done about ventilation and cooling, it’s a gamble to see whether you suffocate before you cook!

Carry that weight.

Before you try this at home, do note that even a small bedroom-sized floating room will weigh the best part of a metric tonne, so make sure that a structural engineer has checked the floor it’s to stand on to make sure your upstairs studio doesn’t suddenly arrive downstairs…

Shape & Design.

Ok, so the floating room is in – and it sounds awful! What went wrong?

Well nothing – if you stop all the sound getting out, then it’s just going to rattle around in the room, meaning that we now have to do some serious manipulation of the room’s internal acoustics to get us back to a ‘normal’ sounding room.

Before we start to add acoustic treatments to the room, there are three factors we can take into account in the design of the room shape that will help.

Firstly we can make sure that none of the surfaces are parallel – including floor-to-ceiling. There are three frequencies that a room will resonate at, which correspond to the length, width and height. These are the ‘axial modes’. Now if a pair of surfaces is absolutely parallel, they will ring at exactly one frequency. Should the surfaces be offset by around 5 degrees or more, rather than producing a distinct note, they will just produce a ‘lump’ in the bass response; and you can knock that out with a ‘bass trap’.

Secondly we can look at the infamous ‘Bolt Graph’ and see if we can make the dimensions of our floating room fall within the Bolt Area.

The Bolt Area. This graph illustrates room ratios of length to width when height = 1.

Rooms whose ratios fall within the shaded area will exhibit a favourably uniform distribution of modal frequencies ie: the bottom end will be less lumpy…

Bolt assumes our room will be rectangular, but rest assured, applying a 5-degree offset to a Bolt room will further help improve diffusion and axial mode problems. Sadly, very few real rooms will fit into the Bolt area; so don’t fret if you can’t squeeze into that shaded blob. Just make sure you aren’t going the other way and building a perfect cube, where all the axial modes will club together to create the mother of all bass resonances at just one centre frequency!

Thirdly, we can look at the layout of the room internally; at this point we are largely interested in the symmetry of the room from the monitors to the engineers ears, and mating this symmetry with an ergonomically useable layout. I will deal with the symmetry issue in the next section, but this further illustrates how the design of a control room needs to constantly balance the competing needs of isolation, acoustics and ergonomics; after all there’s no point in having a quiet, great sounding room, if you can’t reach the gear to work in it!

Room Acoustics.

Our aim is simply to create a room whose characteristic sound we understand almost instinctively. Hardly surprisingly, it appears that the sort of room we understand is one whose sound characteristics closely ape those of an idealised domestic sitting room. In brief this will entail a shortish reverb (or RT60) time (typically in the RT60 range of 0.15 to 0.35 sec) in the midrange. It is considered acceptable for high frequency RT60 to be reduced by up to 50 percent from this figure, and also for Bass RT60 to climb to 120 percent of this figure at 125hz and even up to 180 percent at 63Hz.

Just how a nomad who grew up in a tent (Reverb: non-existent) will relate to such a room design I don’t know, but it does generally seem to work for the rest of us. When I build a control room the best compliment I can get is someone saying ‘Well it sounds just like any other control room’; then I know I got it right!

Now back to the floating room. You’re about to chuck a load of gear and furniture – almost all of which is comprised of hard surfaces – into a room where the reverb time is already too long by virtue of having stopped all the sound getting out. Consequently in order to mimic the ‘sound’ of a domestic room, we are going to have to introduce a serious amount of ‘soft stuff’ (generally some grade of Rockwool tm covered by hessian) to absorb higher frequencies and mimic the effect of carpet, sofas and curtains, along with some tuned resonant bass traps to level out any bumps in the LF response and others to generally absorb the bass in the same way as the windows, doors and ceiling etc were before we stopped them.

Good reflections (and bad ones).

We also want to provide a symmetrical acoustic environment from the speakers to the engineers ears. Why? Well for example if there’s a window one side, then to the engineer the speaker that side will seem to be ‘brighter’ by virtue of the extra reflected sound coming off the window. Hence all the mixes done in that room will sound ‘toppy’ on the other side, as the engineer unconsciously compensates for the room imbalance. A large void to one side will produce the reverse effect.

The reason reflections are bad news off the side walls is due to the Haas effect. Sound from a speaker bouncing off a wall to get to you has a longer path to travel than the direct sound from the speaker. However, Hass discovered that unless this early reflection path is long enough to introduce a delay of over 50msec (which it never is) then the listener’s brain will not identify it as a reflection, but as part of the original sound. Hence the perceived increase in top in the example above. Also in stereo placement Haas has implications, as the tweeter now appears to be a wide smear of sound stretching from the tweeter to the point the sound reflected off the wall – in other words, you’ll be lucky to merely identify if sound sources are left, right, or centre in such a room, accurate stereo placement would be impossible.

So, the front end of the room will be pretty much all soft trapped for highs and mids. In the past the tendency was to let the rear of the room ‘liven up’ a bit so as not to end up with too short a RT60, but the advent of 5.1 monitoring requires that the rear speakers also are free from early reflections, so control rooms are consequently tending to sound a little deader at the back than they used to.

Bass Traps.

These come in two flavours: tuned and general. The tuned ones are designed to knock out any specific ‘lumps’ in the low frequency response the room exhibits. The general ones are there to absorb bass over a wide range of frequencies and help the low end reverb time of the room return to a suitable low figure.

There are many complex and elegant trap designs in existence, but lets look at two simple ones.

Absorbent Traps. Basically just a lot of Rockwool or foam. And when I say a lot I mean it! If you want to make an effective bass trap centred at 50Hz, then you will be building a trap of solid Rockwool 22 feet deep! Now that’s not feasible in the real world. You might also like to ponder on the efficacy of some of the foam ‘bass traps’ currently on the market that are generally about 2 feet deep, ie with a centre frequency of only 550Hz! Better build your own!

A Limp Membrane Tuned Bass Trap. A series of these will typically cover the majority of the rear wall of a studio.

Tuned ‘Limp Membrane’ Traps. Works a bit like a drum. A flexible membrane (usually plywood) at the front of a solid heavy box resonates centred on a frequency determined by the mass/sq metre of the ply and the depth of the box. 100mm or so of Rockwool at the back of the trap does the absorbing for us. A 50Hz trap to this design would be around 450mm deep – that’s more like it!

A General Bass Trap. A pair of these will usually be positioned in the corners facing the main monitors.

Add more Rockwool, and the trap sucks harder, but at less of a specific frequency (a bit like turning the ‘q’ down on a parametric eq). So if we build the trap in a corner (where the depth varies) and fill it full of Rockwool, then it is now a ‘General’ bass trap, absorbing all low frequencies.

Building Regulations.

As of this July an important new set of building regulations has come into force. Called Building Bulletin 93, this regulation has to do with acoustics in schools, but in the process it lays down specific strict criteria for the acoustic performance and isolation of recording studios in schools. This set of specs can be a useful benchmark to aim at if you are building a studio yourself. Note that currently the vast majority of educational studios do not meet these specifications, a situation which many schools and colleges are unaware of – so don’t be tempted to copy their designs! Theoretically such studios could be subject to enforcement if found to fail to meet the criteria. Expect the quality of educational studios to start to improve over the next few years!

And in summary.

So, there you have it. How to build a studio? Of course not! In an article such as this I can only scratch the surface of such a complex subject, but hopefully I have given you some insight, and unravelled a few myths along the way.

If you are about to embark on a studio build yourself, make sure you are fully aware of your construction methods and also fully understand why you are following those specific techniques. Sadly without the right build methods, it is possible to use all the right materials and get no effective result whatsoever. Call a specialist studio consultant if you are in any doubt. Also if there are any heavy construction elements in your studio design, make sure you have enlisted the help of a competent architect and/or structural engineer.

Howard Turner has over 30 years experience in the studio business, and for the last two decades his Studio Wizard Organisation has allowed him to stop shouting at musicians and going to sleep on the mixing desk all of the time, instead he gets to design studios and shout at builders for a change… Further information: 07092 123666 web: www.studiowizard.com

Tech Terms.

RT60: The time taken for the level of reverberation to fall to 60 decibels below it’s peak level.

Axial Mode: The resonant note created by two parallel surfaces.

dBa: A decibel measurement scale commonly used in the building industry. This scale is heavily weighted towards the frequencies of human speech. Consequently manufacturers acoustic specs on building materials are usually only good for this limited midrange bandwidth. As a result, the published figure for a standard wall construction might look good on paper, but when you fire a kick drum at it it’ll probably go through it like it wasn’t there.

dBc The scale we wish everyone used! This is unweighted; ie it measures accurately at all audible frequencies.

The myth of the eggboxes.

Materials that absorb sound actually allow the vibrating air into their structure, where the molecules collide with the absorbent material, converting the sound energy into heat energy. Hence stiff, hairy Rockwool and dense open cell foam (the sort you can blow through) both fit the bill as suitable absorbing materials.

What matters is the thickness of the soft stuff. If we are generous and say that the lowest frequency a material is absorbing effectively at is one with a wavelength 8 times the materials thickness (1/8th wave) then we can see that 50mm of Rockwool will be effective down to around 850Hz (divide speed of sound in air: 340m/s by thickness in metres x8: ie 340/0.4=850); not bad.

On the other hand carpet (thickness 6mm) runs out of steam at 7kHz, and egg boxes (thickness 3mm) are useless below 14kHz! Forget about them as treatment materials!

NC Curves.

Studio gear is getting noisier. Fans and hard-drives make it harder than ever to achieve the sort of quiet we need to be able to monitor effectively, or self-op a vocal or acoustic instrument in the control room. The accepted way of defining noise is by NC curves (illustrated above). The NC measurement of a room is the curve which the background noise never exceeds. We should expect to find NC20-25 in a control room, NC15-20 in a live room and as little as NC5-10 in a voice over booth. With a noisy PC and a fan cooled desk, you’ll be struggling to make NC45-50! So; you monitor loud to hear the detail over the background noise, your ears get tired, you get deaf and your neighbours get tetchy. Time to build some silenced cabinets! (but that’s another story)…

Today I visited a client who had purchased £500 worth of soft material bass traps from a ‘reputable’ company. Each was around 600mm x 1200mm – 3 traps in total.

These traps were advertised to have function in the range of 40-600Hz, but as we can see, they have no significant function below 500Hz. Bearing in mind that a room will generally need to see corrections of greater than 3dB (otherwise, why would the operator even notice it was wrong?), then the fact that these alleged ‘wide range’ traps are only capable of occasional 3dB changes over very narrow bands in the top of the LF range shows that effectively these traps DO NOTHING to the sound of the room.

Before we tested we removed an old double mattress from the back of the room – I’d put money on the fact that that old mattress was absorbing more bass than these flimsy little traps!

So there you have it – the King is wearing no clothes, and the Studio Wizard told you first.

I’ll be loving the comments on here when they come! ht

About the Author:

Howard Turner has over 30 years experience in the studio business, and for the last 2 decades, his Studio Wizard Organisation have been at the forefront of the development of effective & affordable designs and solutions for studios. We design and troubleshoot studios worldwide. Further information: +44(0)7803666789 web: www.studiowizard.com

Your monitors want to tell you something – but are you listening – and more to the point – is it the truth? Howardhacks through the monitoring myths to help you hear what’s really happening.

Your monitor speakers are the most important investment you can make in your studio. Really. Bar none. They are what let you judge your material; they are your quality control.

I’ve heard stunning recordings done on a cassette 4 track – with decent monitors attached. And I’ve heard the results of hundreds of thousands of pounds of gear and time ruined by reliance upon rough, or badly installed, monitoring.

It can be ProTools or an Edisonwax cylinder, Nuendo or Logic, but if you can’t hear what’s going on, then you’re up, as the German’s call it, ‘Scheissen Strasse’…

Studio Monitor or HiFi Speaker?

First of all, lets get one thing straight. Studio Monitors and HiFi speakers have very little in common other than being made of (mostly) wood and having wobbly plastic bits on the front. A HiFi speaker is usually built to the following brief; it must be:

Flattering to the programme material – hide shortcomings.

Sound rich and full (so it uses harmonic ‘tricks’ to make things sound good and to extend the apparent bass response).

Be cheap to produce.

It also is never expected to have to playback anything other than nice, mixed, compressed finished material – no solo’d kick drums here!

As a result your average 100w RMS HiFi box has a tweeter rated at (if you’re lucky) 3 or 4 watts. This is going to burn out the first time a decent lump of feedback or high square-wavy synth is chucked at it! Also it was never designed to be run at anything like rated power for more than a few minutes at a time.

Your studio monitor is a different beast altogether, it’s design brief is to:

Tell the truth, even when it’s painful.

Show up every bit of programme distortion.

Deliver accurate bass within the constraints of the cabinet size.

Be able to survive feedback and high transient impulse noise.

Be capable of running at rated full power for extended periods.

It’s also likely to have a minimum of a 50 watt tweeter in a 100 watt speaker.

By making everything sound ‘nice’ the HiFi speaker is making mixing almost impossible. And it’s going to blow up.

Now that those Japanese hifi wonders are safely in the dustbin, what sort of studio monitors are going to be best for you?

Nowadays, there are almost as many new manufacturers making monitors as there are producing microphones, and inevitably, some are great, some are not so great, and a few are little more than horrid HiFi speakers in disguise; beware! Buy with your ears…

Get active.

Monitor speakers can be divided up in two different ways, firstly there are either 2 driver and 3 driver (or more) systems, secondly, but possibly even more importantly, there are either active or passive speaker systems.

Unless a speaker is tiny (and therefore very quiet) it is impossible to manufacture a single speaker capable of producing the raw energy required for bass reproduction (the cone needs to move a long way) and the fast changes of direction required for treble (transient) reproduction. Consequently speakers come with different drivers each coping with a small part of the frequency range, a great idea until we try to cope with managing how just the right part of the frequency spectrum goes to each driver.

Passive systems take a speaker level feed from a separate power amplifier. The signal is then split by a passive (unpowered) crossover to (hopefully) feed the right bits of the signal to each driver. As the whole splitting thing in a passive speaker is done with high(ish) voltage, high(ish) current speaker level signals, then the technology is of necessity crude and almost Victorian – all coils, fat capacitors and big wire resistors – impressive, but none too subtle when it comes to fine tuning the speaker to the room…

A ‘proper’ active system splits the signal at line (mixer) levels, with a great degree of finesse – the split signal is then sent to several dedicated amps each working with, designed for, and damping, it’s own driver. Accurate crossover control is therefore available with small line level signals easily being manipulated much like the signals in a mixer, and a good match to the room is easily achievable. Sadly a lot of passive speaker manufacturers have jumped on the active bandwagon by bolting an amp on the back of a passively crossed over speaker and calling it active – beware! If it hasn’t got an amp per driver – it’s not active – it’s a passive design in drag!

All those Drivers

The driver issue is one that also has great influence on the output of our studios. We are all used to the sound of domestic 2 driver speakers, which, as they crossover the sound between the woofer and tweeter at around 2 kHz, are consequently distorting the sound at this point, causing a blip in the frequency response curve right at the critical point where lies the bite of the snare, the rasp of the vocal, and the snarl of the guitar etc. As a result it is easy to overcook these things on a 2-driver system, resulting in mixes that are painful to listen to on car hifi, pa systems and the like. A 3-driver system with a midrange driver dedicated to these critical frequencies creates two crossover points one above and one below the critical 1-2kHz region, giving a more faithful reproduction of the important speech frequencies. This may well sound over-middly at first (to our ‘2 driver’ ears). We need to ‘unlearn’ the conditioning of listening to 2 drivers and start to listen to these 3 driver systems as though we are in the room with the musicians. Once you have acquired this ability – the difference in perception is astounding!

Subwoofers.

A natural extension of a multi driver system is to dedicate a speaker and amp to the frequencies that are too low for the main cabinets to handle – this is a Subwoofer, and (owing to the fact that we have a hard time telling where bass noise is coming from) this should be capable of being situated anywhere in the room. Realistically, the Sub still produces frequencies that yield some positional information, so sticking it anywhere is an old wives tale – you’ll need to place it centrally and at the front. With the advent of 5.1 surround monitoring systems, the sub has been pressed into use carrying the ‘FX’ or ‘earthquake’ information too, placing additional constraints on sub placement. 5.1 is a topic in itself, so discussion of surround monitoring will be the subject of another post in the future.

Amps & Cabling

If your speaker system is passive, or a big enough active system, then the amps (and in the case of the active system the crossovers too) will probably be mounted remotely in a rack somewhere. This helps get rid of fan noise from big amps, but it also raises two more issues; amp power and speaker cabling.

Power:

If you buy amp(s) separately from a speaker system, make sure they are big enough. In contradiction to the strange HiFi rule where the speakers should have twice the power rating of the amp, in studios we accept that the amp should have double the rating of the speakers! This is because if the amp goes into distortion, the majority of the distorted signal will route to the tweeter – probably frying it in the process. My old Phase Linear 400 pro amp from the early 70’s is 200watts RMS/channel, but when the meters read 0vu it’s pumping out just 45watts – the rest is headroom…

Cabling:

When the signal from an amp forces a bass driver forwards, it doesn’t want to stop when it gets to the other end of its travel. The cone over-run generates a small electrical signal, which gets back to the amp, which in turn generates feedback to suppress this over-run. If flimsy wires are used between amp and speaker, the resistance of the wires will hinder this damping, and the consequent cone overrun will make the bass sound muddy, so speaker cabling needs to be massive & low resistance. I’m going to be shouted at for the next suggestion, but having done many technical and subjective tests over the years, I can confidently assure you that in most situations the best and most cost effective cable to use between an amp and a speaker is 2.5mmsq T&E solid ring main cable. It ain’t sexy, but it’s cheap and it works brilliantly – in some cases noticeably better than some ‘audiophile’ products costing hugely more.

Stands & Soffits

When amps were weak, and speakers couldn’t handle the power, then the only way to get high volume at low frequencies was to ‘soffit’ mount the speakers actually in the monitor wall, which has the effect of lifting the bass end by some 6-9dB. Individual monitor walls tended to colour the speaker such that consistent results were rare. Nowadays this practice is only required in the largest and loudest pro studio installations. Elsewhere speaker and amp designs are now more than capable of producing the bass we need without help.

What we do need, however, is to support the speaker rigidly. If the room is well designed, then the speaker can be happily coupled to the room by a simple rigid, heavy stand; hollow timber filled with sand, a brick column or the like. If the room is resonant or leaky, then spikes must be employed to cut down structure-born transmission of bass.

Placement

Old fashioned speakers with horn loaded tweeters were designed to focus all the HF information into a ‘sweet spot’ where you HAD to sit to make any sense of the sound, and to get a stereo image. Engineers and producers used to have to fight to occupy that precious football-sized spot during a mix or a cut! Luckily modern dome tweeter speakers are designed for a wide, even dispersion of sound, allowing everyone in the room to hear something (tonally) close to what’s happening in the sweet spot, even if they don’t get the stereo, and also creating a much larger sweet-spot to boot.

For stereo, there are some simple rules regarding placement that will ensure you make the most of your speakers:

1) The speakers and listener should be at the 3 corners of an equilateral triangle. If the speakers are too far apart you will have a ‘hole’ in the centre of the stereo image. In fact with modern dome tweeters you can stretch this rule a bit. In the diagram below you can see that domes produce a decent sized elliptical sweet spot, so by careful placement you can put the engineer at the front of the spot and make room for others to squeeze in behind for critical listening.

2) The ‘virtual source’ of the sound should be at ear height. Yeah, but when you are standing or sitting? If you only ever sit to mix, then around 1300mm is a reasonable height (measure the floor to your ears if you’re not sure). If you mix a lot standing, then raise them up to an in-between compromise height (between 1500-1600mm for instance).

3) Keep the drivers vertically oriented to get the best stereo image. I know you like the look of them when they’re on their sides, but you’ll get much better stereo if they’re upright – trust me!

Virtual Source. A typical 2-driver monitor speaker in vertical orientation, showing the position of the virtual source (i.e. the position the sound appears to emanate from). (Image courtesy of Genelec).

Stereo Monitor Placement. Showing the equilateral triangle of placement and the elliptical ‘sweet-spot’.

Lend me your ears…

Finally, don’t forget that you never listen to your speakers alone. You always listen to them in a room. Consequently the design & layout of your control room can make, or ruin, the sound of your monitors. If you get a chance to listen to some professionally designed rooms, you will see just what I mean!

About the Author:

Howard Turner has over 30 years experience in the studio business, and for the last 2 decades, his Studio Wizard Organisation have been at the forefront of the development of effective & affordable designs and solutions for studios. We design and troubleshoot studios worldwide. Further information: +44(0)7803666789 web: www.studiowizard.com